Recently, there is a demand for improvement of fuel economy (fuel consumption rate) in internal combustion engines from a viewpoint of reinforced control on emission of a carbon dioxide gas and concerns on fossil fuel depletion. Thus, there have been attempts to achieve the improvement of the fuel economy by reducing various types of losses in the internal combustion engine. In general, it is possible to decrease the output required for operation of an engine when the losses are reduced, and thus, it is possible to decrease the minimum output of the internal combustion engine. In such an internal combustion engine, it is necessary to control and supply fuel to the small quantities of fuel corresponding to the minimum output.
In addition, a downsized engine, which acquires size reduction by reducing displacement and obtains output using a supercharger, has drawn attentions in recent years. In the downsized engine, it is possible to reduce a pumping loss or friction by reducing the displacement, and thus, it is possible to improve the fuel economy. Meanwhile, it is possible to obtain the sufficient output using the supercharger and to improve the fuel economy by minimizing a decrease in compression ratio accompanying the supercharging through an intake air cooling effect by performing in-cylinder direct injection. In particular, a fuel injection device using this downsized engine needs to be capable of injecting fuel over a wide range from the minimum injection quantity corresponding to the minimum output due to the low displacement and to the maximum injection quantity corresponding to the maximum output that is obtained by the supercharging, and there is a demand for expansion of a control range of the injection quantity.
In addition, there is a demand for minimizing of the total quantity of particulate matter (PM) during mode traveling and the particulate number (PN) as the number thereof of in engine along with reinforcement of the emission control, and there is a demand for a fuel injection device which is capable of controlling a minute injection quantity. As a means for minimizing the generation of particulate matter, it is effective to perform injection by dividing spray during one combustion stroke into a plurality of times (hereinafter, referred to as divided injection). It is possible to suppress adhesion of fuel onto a piston and a cylinder wall surface by performing the divided injection, and thus, the injected fuel is easily vaporized, and it is possible to minimize the total quantity of the particulate matter and the particulate number as the number thereof. In an engine that performs divided injection, it is necessary to divide fuel, which has been injected at one time so far, to be injected a plurality of times, and thus, it is necessary to control the minute injection quantity in the fuel injection device as compared to the related art.
In general, the injection quantity of the fuel injection device is controlled by a pulse width of an injection pulse to be output from an engine control unit (ECU). The injection quantity increases as the injection pulse width increases, and the fuel injection quantity decreases as the injection pulse width decreases, and the relationship thereof is substantially linear. However, when the injection pulse width decreases, a region with an intermediate opening where a movable element and a fixed core does not collide with each other, that is, a valve body does not reach the maximum opening is formed. Even if the same injection pulse is supplied to each fuel injection devices of cylinders, the displacement quantity of the valve body of the fuel injection device greatly differs depending on an individual difference caused by dimensional tolerance of the fuel injection device or influence due to deterioration with age in the region with the intermediate opening, and thus, individual variations of the injection quantity are generated. In addition, even when the quantity of displacement of the valve body is equal, the individual variations of the injection quantity are generated due to the influence of the dimensional tolerance such as an injection hole diameter of an injection hole to inject the fuel. Since the required injection quantity is small in the region with the intermediate opening, the influence that the individual variations of the injection quantity on a degree of homogeneity of air-fuel mixture becomes more significant, and there is a problem in using the region with the intermediate opening from a viewpoint of stability of combustion.
In addition, minimizing of the fuel injection quantity variation in the region with the intermediate opening where the injection pulse is small and the valve body does not reach the maximum opening and accurate control of the injection quantity are required in order to significantly reduce the minimum injection quantity.
A technique, which is capable of detecting a fuel injection quantity variation, generated due to the dimensional tolerance of the fuel injection device, such as an individual difference of time between stop of the injection pulse and arrival of the movable element at a valve closing position, for each fuel injection device of each cylinder and correcting the injection quantity for each individual device, is required in order to reduce the fuel injection quantity variation at the intermediate opening. There is a method disclosed in PTL 1 as a means for detecting an operation timing of a valve body of a fuel injection device which is the main factor of a fuel injection quantity variation. PTL 1 discloses the method of detecting a valve closing finish timing of the valve body by comparing an induced electromotive voltage generated at a voltage of a coil and a reference voltage curve, and determining a valve closing time of an injection valve based on the detection information.
In addition, there is a case in which deposits adhere to the injection hole to inject the fuel, and the injection quantity changes due to the influence of the dimensional tolerance of the injection hole diameter of the fuel injection device or the deterioration with age. Such deposits may be generated when soot generated by combustion enters the injection hole or when the fuel is deposited around the injection hole and becomes the deposits. In this case, the fuel injection quantity variation is generated even when a time-series profile of the valve body of the fuel injection device of each cylinder is the same, that is, each valve closing finish timing is the same. For example, PTL 2 discloses a method of detecting a fluctuating waveform caused by fuel injection by detecting a time-series profile of a pressure sensor in an ECU using a pressure sensor arranged on a side close to an injection hole with respect to a common rail, and estimating an injection quantity based on the detected waveform.